Dear Darioush,

Trials are still ongoing and there are already some scarce reports on the fact that collagen might play a role in diabetic ulcers. 

This year there has been a report of a case series of six patients that you may be interested in:

Miller JD, et al. Use of collagenase ointment in conjunction with negative pressure wound therapy in the care of diabetic wounds: a case series of six patients. Diabet Foot Ankle. 2015 Jan 27;6:24999. doi: 10.3402/dfa.v6.24999.

It has already been proven in experiments on animals that collagen dressing are effective on diabetic wounds:

Moura LI, et al. Neurotensin-loaded collagen dressings reduce inflammation and improve wound healing in diabetic mice. Biochim Biophys Acta. 2014 Jan;1842(1):32-43. doi: 10.1016/j.bbadis.2013.10.009.

Nevertheless, it appears that data are very scarce up to date. I am attaching you the two papers mentioned above.

Best Regards,

Ilir Alimehmeti

http://diabeticfootandankle.net/index.php/dfa/article/view/24999

http://www.sciencedirect.com/science/article/pii/S0925443913003049

I think it's better for cells migration and proliferation. 

Collagen would act as substrate for MMPs developed in the diabetic wounds, thus reduces the attack of MMPs on native collagen matrix. In addition the degradation products have significant role in cell proliferation and migration of fibroblasts.